The present invention relates to locks and more particularly to "electronic" key locks of the kind comprising: a bolt; a rotatable thrower for retracting the bolt; an electromechanical release mechanism which normally prevents retraction of the bolt when thrown but which can be actuated to permit such retraction; a rotatable barrel defining a keyway to receive and be turned by a proper coded key; reading means associated with the keyway for electronically transducing the code from a proper key; and processing means to receive the code transduced by said reading means and to issue a signal to actuate said release mechanism upon the recognition of a correct code.
Electronic key locks are well known, at least in the patent literature, and have been proposed in conjunction with diverse methods of key code detection. It is recognised that, both in the interests of user acceptance and to maximise the utilisation of standard lock components and furniture, the overall appearance, dimensions and functionality of such locks should resemble those of conventional mechanical key locks as far as practicable. A universally known style of mechanical key lock is the conventional cylinder lock, comprising a main casing which houses the bolt and which receives a locking cylinder unit through an aperture therein. The cylinder unit comprises a barrel journalled in the cylinder body and normally blocked against rotation by a series of mechanical tumblers extending across the shear line, but which can be freed for rotation by the insertion of a properly profiled key. At the rear end of the cylinder unit, where it is received within the main casing, the cylinder body bears a thrower (frequently termed a cam) to which the barrel is coupled and the turning of which retracts the bolt.
In the past attempts have been made to embody an electronic key lock in an equivalent structure to that of the conventional mechanical cylinder unit described above. Thus in U.S. patent specification No. 4771620 there is shown an electronic cylinder unit with an equivalent cylinder body, barrel and thrower, but where release of the barrel for rotation is controlled by a solenoid located in the part of the cylinder body which surrounds the barrel and which is actuated in response to the reading of a correct code through electrical contacts on the key. We believe, however, that while meeting the desire for physical resemblence to a conventional cylinder unit, this structure has several disadvantages. Firstly, electrical connections are required from the reading contacts to a processing module outside the cylinder unit and back to the solenoid, which may be difficult to make and vulnerable to attacks. Secondly, it may be possible to attack the lock by forcibly extracting the barrel from the cylinder unit or by forcibly extracting the cylinder unit from the main casing, thus leaving the bolt unblocked and easy to manipulate. Thirdly, the location of the solenoid in the outer portion of the cylinder unit places constraints upon its size, could make it vulnerable to certain kinds of attack and leaves no room in the cylinder body for extra electronics; for example, if a high frequency inductively-coupled key reading system is chosen, it is desirable to have the oscillator circuit for the radiating field as close as possible to the reading head.